MDC1 majorly functions as a mediator in the DDR, which mediates the recruitment of other DDR proteins, such as ataxia telangiectasia-mutated (ATM), Breast Cancer 1, Early Onset (BRCA1), Mre11/Rad50/NBS1 (MRN) complex, to the site of damage [7]–[10]. This evidence concerns the gene ATM and cancer.